The present invention relates to an apparatus for filtering a machining liquid of an electroerosion or spark erosion machine.
Electroerosion machines have a working container filled with a machining liquid in which is immersed a workpiece to be machined by electroerosion. The machine liquid in the case of so-called wire cutting machines comprises pure water or a liquid, the main constituent of which is water, whereas it comprises hydrocarbons in the case of countersinking machines. During the erosion of the workpiece there is a reduction in the machining liquid purity and as a result its electrical conductivity also changes. In order to maintain a given quality of the erosion machining, it is necessary to purify the machining liquid, in order to keep its electrical characteristics and purity within predetermined limits.
Attempts have already been made to use membrane filters in the filtering apparatus for filtering the machining liquid. Thus, e.g. JP-OS 62-24 917 discloses a filtering apparatus with a membrane filter for an electroerosion machine. The filtering apparatus comprises a container for the machining liquid, which is subdivided into two areas by a cellophane membrane. The first area is connected by means of a pump, which is followed by a conventional filter, with the working container of the electroerosion machine and which, by means of a further pump, can be emptied again into the first area of the container. The second area of the container is connected by means of a further pump to an ion exchanger. The ionic concentration in the second container area is in the magnitude range below the ionic concentration in the first container area, so that the ion exchanger can be operated with a low ion density which is advantageous for its operating behavior. In this known filtering apparatus the membrane filter wall merely serves to bring about the adjustable reduction of the ion density for a cycle of an ion exchanger.
For filtering the machining liquid of electroerosion machines, it is also known to use conventional filters with a large mesh size compared with membrane filters.